Data communication networks may include various computers, servers, nodes, routers, switches, hubs, proxies, and other devices coupled to and configured to pass data to one another. These devices are referred to herein as “network elements,” and may provide a variety of network resources on a network. Data is communicated through data communication networks by passing protocol data units (such as packets, cells, frames, or segments) between the network elements over communication links on the network. A particular protocol data unit may be handled by multiple network elements and cross multiple communication links as it travels between its source and its destination over the network. Hosts such as computers, telephones, cellular telephones, Personal Digital Assistants, and other types of consumer electronics connect to and transmit/receive data over the communication network and, hence, are users of the communication services offered by the communication network.
Network elements are typically implemented to have a control plane that controls operation of the network element and a data plane that handles traffic flowing through the network. The data plane typically will have a collection of line cards having ports that connect to links on the network. Data is received at a particular port, switched within the data plane, and output at one or more other ports onto other links on the network. To enable the data to be handled quickly, the data plane is typically implemented in hardware so that all of the decisions as to how to handle the data are performed using hardware lookups, etc.
Two or more links may be grouped to form a Multi-Link Trunk (MLT). MLT is a method of link aggregation that allows multiple point-to-point links to be aggregated together in order to provide a single logical trunk. An MLT provides the combined bandwidth of the multiple links, as well as the physical layer protection against failure of any single link. Each MLT is assigned a MLT group ID (MLT-ID), which is a global value within the cluster and unique across the cluster nodes. An MLT with all its port members only on one node is referred to as a normal MLT group. An MLT group where its port members are on two or more nodes is referred to as a Split MLT or SMLT group. Link Aggregation Group (LAG) uses multiple network cables/ports in parallel to increase the link speed beyond the limits of any one single cable or port, and to increase the redundancy for higher availability. While the description below and the Figures refer to a SMLT, the same concepts apply to MLT and LAG and the terms SMLT, MLT, LAG and MLT/LAG and SMLT/LAG are used interchangeably throughout the rest of the application.